Electrostatic charging means and method



Jan. 26, 1960 c. GIAIMO, JR 2,922,883

ELECTROSTATIC CHARGING MEANS AND METHOD Filed March 3, 1955 SUPPL Y z; 7

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ATTORNEY.

ELECTROSTATIC CHARGWG MEANS AND METHOD Edward C. Giaimo, In, Cranhury, N..l'., assignor to Radio Corporation of America, a corporation of Delaware Application March 3, 1955, Serial No. 491,809

6 Claims. (Cl. 25049.5)

This invention relates to electrostatic photography, and more particularly to means for and methods of imparting an electrostatic charge to a chargeable member.

In the art of electrostatic photography, means have been provided for developing an electrostatic latent image on a record member. The record member usually comprises a coating of photoconductive material on a surface which is relatively conductive. When it is desired that the ultimate record appear on a member which is nonconductive, the surface of that member carrying the photoconductive coating must first be treated to render it conductive. Thus, in applying the photoconductive material to a glass support member, the surface is first treated with tin salts in a well known manner to render the surface of the glass conductive While maintaining a measure of its transparency.

In other arrangements, a photoconductive coating was applied to the surface of a sheet of paper. It has been found that better results are obtained with the coated paper during times of higher ambient humidity, the conductivity of the paper backing being higher when the relative humidity is higher. In this type of operation, the paper backing was placed in contact with a grounded metal plate. The surface of the coating is charged by ion bombardment, the ions resulting from the operation of a corona discharge device. Whether the paper type record or a metallic record, both having a photoconductive surface, is used, it appeared that, without a relatively conductive backing member used during the initial charging of the record surface, the ultimate results were not entirely satisfactory. It is believed that the useful effect of the conductive backing was the production of a Zero potential surface at the interface between the photoconductive layer or coating and the backing member.

It is an object of the present invention to provide an improved method of imparting an electrostatic charge to a chargeable member without the necessity of providing a conductive backing for the chargeable member.

It is another object of this invention to provide improved means for imparting an electrostatic charge to a chargeable member.

charge, bombarding the opposite surface of the member 2,922,883 Patented Jan 26, 1960 with positive ions. This arrangement oppositely charges the opposite surfaces of the member, producing, effec tively, a zero potential plane in the interior of the chargeable member without the use of a conductive backing.

A better understanding of the invention may be had from the following detailed description when read in connection with the accompanying drawing in which:

Fig. 1 is a schematic representation of apparatus embodying the present invention;

Fig. 2 is a perspective view of a charging unit constructed in accordance with the present invention; and

Fig. 3 is a plan view, partly broken away, of a corona discharge device of the type employed in the structure illustrated in Fig. 2.

There is shown in Fig. 1 a chargeable member 2 which comprises a coating of photoconductive material 4 on an insulating backing 6. The backing 6 may comprise a paper carrier for the photoconductive coating 4, or may, with equal facility, comprise a backing member in the nature of plastic, glass or mica, for example. The chargeable member 2 is arranged to pass or be positioned between a first corona discharge device 8 and a second corona discharge device 10. The first corona discharge device 8 comprises three parallel fine Wires 12 which are connected. to a high voltage supply 14 which is adapted to apply a high negative voltage to the three Wires 12. Similarly, the second corona discharge device comprises three parallel fine wires 16 which are connected to a high voltage supply 18. This high voltage supply 18 is adapted to apply a high positive voltage to the wires 16. It will be appreciated that suitable means (not shown) are provided for supporting, guiding or holding the chargeable member between the two discharge devices. Thus, a zone of one surface of the chargeable member 2 is exposed to a corona discharge of one polarity and a zone opposite the first zone of a surface opposite from the first surface is exposed to a corona discharge of opposite polarity.

The high voltage applied to the first corona discharge device results in the production of a negative corona discharge which in turn includes the generation of a cloud of negative ions. Similarly, the high voltage applied to the second corona discharge device results in the development of a positive corona discharge which in turn produces a cloud of positive ions.

Surrounding the corona discharge device is a metal shield member 20. This metal shield member 20 is grounded electrically and serves to confine the corona discharge or ion cloud to the operating area. The shield is provided with slots 22 through which the chargeable member 2 may be passed in its passage between the two corona discharge devices.

In Figs. 2 and 3, there is shown a charging unit which was constructed in accordance with the present invention. The corona discharge members are shown more clearly in Fig. 3 and comprise an insulating support member 24 of a suitable plastic material such, for example, ac Lucite. The support member 24 is substantially rectangular in shape and is provided with a large central opening 26. Three fine wires 28 are stretched lengthwise across the opening 26. The wires 28 may be made of tungsten .001 of an inch in diameter. These fine wires are supported by springs 30 which pass through suitable holes 32 in the ends of the support member 24. The springs provide sufiicient tension to maintain the wires tautly stretched across the opening 26. The outer ends of the springs are connected to a relatively heavy bus wire 34 which serves both to hold the springs in position and to carry the voltage from the voltage supply through the springs 30 to the wires 28.

Two of these support members together with their wires and carrying means are mounted in a framework which includes two side panels 36, a top panel 38 and a bottom panel 40. These four panels constitute the shield 20 shown in Fig. 1. Each of the two side panels 36 is provided with a transverse slot 42 through which the chargeable'member 2 may be passed. Thus the two panels with their slots define a path of movement for the memher beingcharged. The two side panels are coupled together through suitably placed spacer members 44. The two side panels have a pair of vertical slots 46 adjacent the ends of the panels. Thetwosupport members 24 are adjustably mounted on opposite sides of the slot 42 by means of a set of screws 48 which extend through the vertical slots 46 and into suitable holes 50 in the support members. Similarly, the top panel and the bottom panel are adjustably supported between the two side panels by a set of screws 52 which extend through the vertical slot 46. With these elements adjustably supported with respect to the lateral slots 42, the relative positioning of the elements may be adjusted to give optimum results with various types of record materials or chargeable members.

In a successfully operated unit constructed in accord ance with this invention, suitable chargeable. members have been satisfactorily charged when the corona discharge devices were spaced between A inch and 1 inch, approximately, from the opposite sides of the chargeable member and the voltages applied to the corona discharge devices were on the order of 4,000 to 6,000 volts. With apparatus thus provided, photoconductive coatings have been suitably charged with the coating being carried by a paper backing member, by a glass backing member and by a mica backing member. All of these were suitably charged without the necessity of providing a conductive medium between the photo-conductive surface and the insulating carrier member. Further, it has been found that with apparatus of the type described, a more uniform initial charge may be applied to the chargeable member, and, in the case of electrostatic photography, the relative charging of the opposite faces of the record member may be controlled to effect a control of the contrast in the ultimate print.

What is claimed is:

1. Means for imparting an electrostatic charge to a chargeable sheet member comprising a first corona discharge device including a first nonconductive support member and a plurality of spaced, parallel fine conductive wires carried by said first support member, a second corona discharge device including a second nonconductive support member and a plurality of spaced, parallel fine wires carried by said second support member, means for mounting said support members in opposed spaced, parallel relation directly opposite to each other, and a conductive shield surrounding said spaced support members, said shield having openings therein to define a path of advancement for said sheet member between said first and second corona discharge device.

2. Means for imparting an electrostatic charge to a chargeable member by ion bombardment; said means comprising a first corona discharge device including a first nonconductive support member, a plurality of spaced, parallel, conductive fine wires carried by said first support member and means for applying a high negative electrical potential to said wires; a second corona discharge device including a second nonconductive support member, a plurality of spaced, parallel, conductive fine wirescarri ed by said second support member, means for applying. a high positive electrical potential to said wires carried by said second support member; means for mounting said support members in opposed, spaced, parallel relation; and a conductive shield surrounding said spaced support members, said shield having openings therein to define a path of advancement for said chargeable member betWeen said first and second corona discharge device and means connecting said shield electrically to a point of neutral potential between said high negative and said high positive potentials.

3. In electrostatic photography, means for imparting electrostatic charges to a chargeable member comprising a pair of charging electrode structures located in opposed spaced relation, means for locating said chargeable member between said charging electrode structures, connection means associated with one of said electrode structures for applying thereto a high positive-potential, connection means associated with the other of said electrode structures for applying thereto a high negative potential, a first shielding structureas sociated with said one of said electrode structures, a second shielding structure associated with the other of said electrode structures, and connection means associated with said shielding structures for applying thereto a reference potential between said high positive and high negative potentials.

4. In electrostatic photography, means for imparting an electrostatic charge to a chargeable member comprising a first corona discharge device including a first nonconductive support member and a plurality of fine conductive wires carried by said first support member, a second corona discharge device including a second nonconductive support member and a plurality of fine conductive wires carried by said second support member, connection means associated with said first corona discharge device for applying to the wires thereof a high positive potential, connection means associated with said second corona discharge device for applying to the wires thereof a high negative potential, means for mounting said support members in opposed spaced relation, a first shielding structure associated with said first corona discharge device, a second shielding structure associated with said second corona discharge device, connection means associated with said shielding structures for applying thereto a reference potential between said high negative and said high positive potentials, and means for locating said chargeable member between said corona discharge devices.

5. Means for imparting an electrostatic charge to a chargeable member by ion bombardment; said means comprising a first corona discharge device including a first rectangular nonconductive support member having a central opening therein, a plurality of fine conductive wires parallelly supported by said first support member andbridging said opening therein, and means for applying a high negative electric potential to said wires; a second corona discharge device including a second rectangular nonconductive support member having a central opening therein, 'a plurality of fine conductive wires parallelly supported by said second support member and bridging said opening therein, and means for applying a high positive electrical potential to said wires supported by said second supporttmernber; means for mounting said support members in spaced parallel relation; and a conductive shield surrounding said spaced support members connected electrically to a point of potential midway between said high negative and said high positive potentials, said shield having openings therein to define a path of advancement for said chargeable member between said first and second corona discharge device.

6. In electrostatic photography, means for imparting electrostatic charges to a chargeable member comprising a pair of charging electrode structures located in spaced relation directly opposite to each other, means for locating said chargeable member between said charging electrode structures, means for applying a high positive potential to one of said electrode structures, means for applying a high positive potential to one of said electrode structures, means for applying a high negative potential to the other of said electrode structures, a shielding structure associated with the charging electrode structures, and means for connecting said shielding structure to a point of reference potential between said high positive and high negative potentials.

References Gated in the file of this patent UNITED STATES PATENTS 1,352,699 Smith Sept. 14, 1920 2,042,145 Darrah May 26, 1936 10 2,128,907 Benner Sept. 6, 1938 

